This invention relates to an improved process for treating wool scouring waste liquors which, in addition to being commercially feasible, will significantly reduce treatment costs compared to other presently known commercial methods. The improved process also enhances the possibility of recovering a significant amount of wool grease from the waste sludge, which at today's market prices, makes such a recovery a valuable by-product.
Wool scouring is one of the first steps that must be carried out before raw wool can be used in textile operations. The scouring or washing process is performed to remove the many varied impurities the wool contains. Some of those impurities include dirt, sand, vegetable matter, animal wastes, paint (used in branding), suint (a water soluable material secreted by the animal's sweat gland) and grease (a complex water-insoluable mixture which protects the wool fibers during growth). The scouring process is normally carried out at an elevated temperature, generally in the range of 130.degree. to 150.degree. F, by passing the raw wool through a series of bowls or tanks containing suitable detergents and alkalis, while alternately squeezing the wool by running it between rollers. This process is well known in the art and is almost universal in its application.
The resultant spent waste liquor produced during this scouring process produces one of the most objectionable and polluted wastes known (comprised of as much as one-third of the total solids in the form of wool grease) and its disposal presents significant problems to the textile industry.
The waste liquor is comprised of all the impurities described above, plus the deterging chemicals used during the scouring process. Because the centrifugal separators recover only 25-30% of the recoverable wool grease, the resultant waste liquor may contain 0.5-1.5% of wool grease and other soluable organic compounds. The rusulting waste liquor cannot be, by law, discharged directly into open bodies of water or into municipal sewer systems, unless the waste is treated or conditioned to reduce its chemical oxygen demand (COD), the measure of polution, to acceptable limits.
As the cost of the mandatory processing of wool scouring wastes increase, the economics of attempting to reclaim the wool grease as a valuable by-product also increases as the industry strives to reduce its total operating costs. Historically, only a small percentage of the total wool grease production is ever realized. The reason stems partially from the available technology for grease recovery which have been in use heretofore.
There are several known methods for treating scouring wastes and recovering grease. They include centrifuging, acid cracking and precipitation processes. Of these processes, the most successful results have been achieved using acid cracking in which the waste liquor is treated with suitable acid, usually sulfuric, to obtain pH in the range of 3.5. According to this process, the wool grease, dirt and other solids are permitted to settle out. The recovered solids are then further treated to remove the grease using a vacuum filter or filter press. This filtration process will generally remove approximately 50% of the total available grease from the other solids, making it one of the most efficient processes. The filtration process, on the other hand, is cumbersome and does not lend itself to large commercial operations, because large amounts of filter aid are required to prevent clogging of the filters.